The invention relates to a method for the controlled dimming of an illuminant such as, for example, an LED, OLEDs or gas discharge lamps in accordance with digital dimming values that form desired values.
Such a method is known and is, for example, embodied with the circuit arrangement according to the prior art as illustrated in FIG. 1. In the case of the known circuit arrangement, the illuminant is a gas discharge lamp 1. The latter is operated with a ballast 2 that is embodied in a known way, and for this reason only the important components are illustrated in schematic form. The ballast 2 contains two series-connected electronic switches S1, S2 that are supplied with a normal DC voltage. The two switches S1, S2 are controlled by a digital switching unit 3 that can change the switching frequency and/or the duty ratio. A series resonant circuit formed from an inductor L and a resonant capacitor C1 is located above the lower switch S2. The voltage drop across the resonant capacitor C1 is fed to the lamp 1 via a coupling capacitor C2. There is a resistor in the circuit of the lamp. The voltage drop across the resistor R1 is a measure of the luminous intensity produced by the lamp 1, and can therefore be used to form analog actual values Ia. The lamp 1 is dimmed via a digital control loop. Digital dimming values Dd are made available via a DALI bus, for example, by a dimming value transmitter 4, which can be arranged in a remote control center. Digital dimming values can, for example, be formed by 12 or 13 bits in order to ensure as fine resolution of the dimming stages as possible. The abovementioned analog actual values Ia are converted into digital actual values Id in an A/D converter 6. The digital dimming values Dd and the digital actual values Id are compared with one another in a digital comparator 5. For the comparison, the A/D converter 6 should have as far as possible the same bit number as the digital dimming values Dd. A consequence of this in the case of a relatively high bit number of—as previously mentioned—12 or 13, for example, is that the A/D converter 6 operates relatively slowly. By means of the comparison of the digital dimming values Dd and the digital actual values Id, the digital comparator 5 produces a digital control deviation Xd that is fed to a digital controller 7. The digital controller 7 produces therefrom a digital manipulated variable Xd that is then fed to the digital switch unit 3.
Since, as previously mentioned, the A/D converter 6 is relatively slow, it operates in the range of milliseconds. Consequently, the entire control loop is relatively slow.